Radiation counter



April 24, 1951 c, MARSH 2,550,488

RADIATION COUNTER Filed Oct. 27, 1948 INVENITOR. Char/es P. Marsh BY I A TTOENEY Patented Apr. 24, 19 5 g g i P UNITED STATES PATENT OFFICE A i v V 2,550,488

' RADIATION COUNTER Charles R. Marsh, State College, Pa., assignor to the United States of America as represented by the United States Atomic Energy Commission Application October 27, 1948, Serial e. 56,847

Claims. 1 V 1 My invention relates to radiation counters and more particularly to a pulsetype counter or rate meter circuit for inclusion in a system for use in the detection of alpha and beta particles, gamma jectof his invention the provision of a pulse type rate meter circuit which is responsiveto individual particles of radiation.

Applicanthas as another object of his invention the, provision of a rate meter circuit which 2 will provide audible indication of individual par-'- ticles of radioactive material as they are detected.

Applicant has as another object of his invenrays and slow and fast neutrons in the propor- 5 tion the provision of a system permitting the raptional range, or for use in a system inthe Geiger id survey of places of prospective contamination range, and for otheruses. by making it sensitive to individual particles of ,In the prior art various types of scaling and contamination to provide spontaneous audible rate meter circuits have been employed for the indication thereof. a detection and/or measurement of radiation; The 1; Application has as a further object of his inproportional counter serves as a measure of the vention the provision of a pulse type survey inaverage intensity of radiation. It may employ strument for detecting radiation employing aproan ionization chamber or. other pickup device portional counter and per i the use of an which feeds pulses through conventional ampliamplifier of lower gain for reducing microphony fiers to a pulse equalizer, suchasa multivibrator to a negligible proportion. or univibrator biased to cut off, so that pulses of Applicant has as a still further object of his random size may be'utilized to produce uniform invention e provision f a pulse y p p (generally rectangular) pulses which in turn are tional counter circuit which isespeeially adapted supplied'to, an electrical tank circuit that pro- I to th det tion of w l v l f lph vi y vides the necessary damping forv the meter or in 20 in the p c of high levels of beta a amma dicator. See Review of Scientific Instruments, vol. activity.

7, page 45o. The tank circuit, usually of th jr Other objects andadvantages of my invention sistor-capacitor type, is so arranged that each. will appear from the following specification and pulsetobe counted causes a definite amount of accomp y drawings d t ove features charge to be placed on, the capacitor in ti thereof will be particularly pointed out in the short compared with the average spacing of annexed Claims- 7 pulses. The charge on the capacitor leaks off In the draw s the Sole fi u c oses a through thehigh resistor, making the average Schematic f a p l p rate met C cuit to potential across the capacitor proportional to the provide audible indication of individual particles counting rate, and thus proportional to the acf adi tivity of the radioactive sample. Improvements The Circuit of the present invention is ordihave been made in this basic circuit by reducing neiily p yed to p du udible indications bulkiness, through elimination of batteries, and or clicks in the output of a loud p a e 0 V by increasing the counting range, of the in trusound reproducing device when radioactivity is month See Review of Scientific Instruments, vol. d t t d by a urv y probe Vari us ypes of sur- 17,1 page 323'. However, no provision has been v yprobes, such as hose disclosed in the comade for response to individual radioactive par- Pe app i a of Borkowski, ticles, or for any spontaneous audible indication 748,433, filed y 1947, y be utilized, and of the'existence of these particles. In addition, the ut t f h u v y p e t s w ay the above systems are sluggish and slow, and only d th a v al p fi r of p f provide an average response. They are not suit- 40 y three Stages (not w the i put I of ed tothe detection of low levels of alpha activity the pulse circuit shown in the draw I However, in the presence f high b t nd gamma, ti the tubesof the amplifier are preferably biased ity. 'Due to the high amplifier gain required and to operate in a ar a nei". I attendant microphonics, pulse ion chambers have put I feeds the control grid 3 f a gas been found impractical as alpha survey instrutetrode 2 through condenser 4 Which s a p of Inents. In addition the instruments must be the conventional resistance up mpl y d closely followed, and visibility must be such at between the last'stage 0f the usual a pl fier o all times that the average radiation may be read, shown) and the pulse circuit. Negative bias for Applicant with a knowledge of all these defects grid 3 i furnished from the B pp y S u ce 5 in and objections to the prior art has for an ob- 5 through voltage divider 6 and resistor 'I. This is accomplished by placing the cathode of tube 2 at ground potential and maintaining B(-) at some selected point below ground, such as This voltage, of course, is determined by the' constantsof the circuit, and to aid in-the volts.

3 maintenance of this potential, a voltage regulator tube 8 is shunted across voltage divider 3. The negative bias normally holds the tube 2 in a non-conducting state. A positive pulse through input circuit A which is greater than the difference between the bias and that necessary for cutoff fires the tube Signals less than the threshold voltage, that is, the difference between the biasing potential and that required for cutoff, are rejected, thus effectively eliminating spu. rious pulses due to tube noises, microphgnicdisturbances, and the induced voltages from firing the tube. A pulse high enough. to. fire. thev tube causes a charge to be ti'ansniittedgthrough' it which is independent of the size of the trigger-v ing pulse.

Potential is applied to the anode of tube 2 by.

condenser 9 which is coupled thereto through in ductance or reactance 10. preferably about .i mfd and is bridged across the inductance Ill and the cathode of tube 2. The screen grid l l is also maintainedat ground potential and acts as a shield. A charge is built up on condenser 9 lllflllOllghIQSlSllQlli l2, primary of transformer l3, from condenser Li and ultimately from B of source 5. Resistor l2 and condenser 9 cause tube 2 toact somewhat similar to a relaxation oscillator. Condenser Hi may have as great as to times the capacitance of condenser 9 and thus tendsto hold, the lower end 21; of the primary of transformer l3 at a substantially uniform A. C. potential. It, is bridged across the circuit between thelower end 21, of the primary winding oftransformer, 13 and. ground so that point 27 has B(+) potential equal to thatof supplyvoltage minus. IR. loss. across.v resistance 15. I is. a linear or quasi-logarithmic. function of frequency. The..-t ransformer I3. is. preferably a 5000/4. ohm 5. Watt output. transformer.

Condenser. 1.4- ischarged up. from source through resistor i5 and meter l6. Shunts suchas resistors 17, I8. may beemployed by actuating selector switch [9 toincrease the range of the meter l6 inthe usualand. well known manner. In additiona large condenser 211, preferably of the electrolytic type of the order 1001000 mfd., may be shunted-across the meter IB for damping purposes. The selection of the condenser size, of course, will depend upon the damping desired, and the meter employed.

As a protective measure for preventing injury to the meter l6-a neon tube 2! is bridged across the resistor I5 and meter I6, that when the meter reaches a full scale reading the drop across, the resistor I E-"and meter IE will equal the striking voltage of the neon tube 2|. This neon lamp provides visual evidence of I radioactivity sufficient in intensity to cause full scale deflection, and is more rapid in response than the damped meter. This feature can be important in noisy areas. The well known characteristics of a neon tube which enable it to maintain a constantpotential while passing a varying current permitit to also act as a voltage regulator when the threshold potential is reached so that injury to the meter may be obviated. Voltage regulator tubes 22, 23 may be connected in series and employed to maintain the potential regulationbetween the anode with respect to ground, and theresistor 24'may be inserted to absorb variations in power supply voltage.

In operation, the negative control grid bias normally holds the tube 2 in a non-conducting state, and as indicated heretofore, a positive pulse of a predetermined sizefires thetube 2 and discharges h apacitor s 4 the condenser 9 as described more in detail here inafter. By making the time constant of the grid circuit small and having the bias several times more negative (greater) than cutofi bias, the largest pulse which the preceding stage will transmit is reduced to less than triggering Voltage within the time constant. Since the tube 2 will still be conducting at this. time, variations in pulse height will have no influence. A pulse height sufficient to fire the tube 2 transmits through it a charge independent of the size of the triggering pulse. The charge is a function of the capacitance of condenser 9, the voltage across the pair of voltage regulator tubes 22, 23, less the IR dropacross the recharging network and the tube pulse on its control'grid 3, the condenser 9 discharges through it. Inductance i E! is provided to flatten out the dischargecurve of the condenser 9, making it more sinusoidal and causing thepotential on the plate of the tube 2 to drop below. the tube extinguishing. potential sothat the con.-. trol grid 3 may regaincontrol of the gas tube 2.

It isimportant that the'grid. be able-to regain control of tube 2 after each, pulse. or group of pulses. By properly choosing the values of.- the anode condenser 9, RF'choke lfi' andlrecharging resistor. [2, the tube will always oscillate when in discharge, and the grid. willzbeable to cutoff the tube at the desired anode current minimum. Condensers of .1 mid, chokes. of 1-5. mhy., and resistors of 15-20 K are suitable.

After tube 2 ceases to conduct and condenser 9 commences to charge up again through resistor l 2, substantially. full B potential I of around 300 volts appears across the parallel capacitor 25, resistor i combination andthe .primarywinding of transformer [3, whose secondary feeds the speaker 26, in the form of a surge. The capacitance of the by-pass condenser-25; is-preferably about one-half of that ofcondenser 9, so that its impedance at the surge frequency maybemade negligibly small when compared to that of the 7 primary of transformer l3 and as a resultmost of the voltage ofthe rechargingsurge for con denserfiappears across the primary winding, andthrough transformer action prioduces a sharp click in the speaker-N connected to thesec Inthe above arrangement it willbe noted that the condenser l charges up throughresistor l5 and meter is from source 5, and discharges through primary of transformer lt andcondenser 25, resistor l2 combination to chargecondenser 9, in the manner describedabove. The recharging current for condenser I4 is indicated by thedamped microammeter l6 whilethe network of the. transformer primary and resistor-condenser combination act asatwo section lowpass filterto integrate the recharging current and provide an audible indicationof such recharging.

While the power source 5,.is only schematically; shown and the, heater supply for, theQfilament of tube 2 is notindicated, onesuitable'seurce, among other known sources, may provide, 3H5...volts. at.

10 milliamperes for theamplifier and,- rate-meter,

and1000-3000 voltsat 5 microamperes for the probe or survey instrument. A voltageregnlator tube may be employed ;to regulatetheformer, anda 15 va. constant voltage. transformer. may. beemployed, to; supply thegprimary of the. highvoltage To. compensate; for. distortion the transformer, potential from the filament supply maybe added in phase to the transformer. In addition other known stabilizing features may be employed. :f

Although the foregoing pulse circuit is similar in many respects to a relaxation oscillator, it is so biased that it acts instead to assure a flow through'the meter it of current which varies as a function of frequency only, being very nearly independent of pulse magnitudeand shape Within the usual limits. This also insures against the drift of zero frequency reading on the frequency or rate meter.

"Having thus described my invention, I claim:

1 ,A pulse circuit of. the character described comprising a' normally inoperative gas electric discha'rg'e'device, an output circuit for said discharge device including a resistor and a capacitor for intermittently discharging through the discharge device and recharging through said resistor, means for coupling said output circuit to a sound reproducing device, means for periodically rendering said discharge device operative,

and means providing a low impedance surge path about said resistor when said capacitor charges for producing pulses across said sound reproducing device.

2. A pulse circuit of the character described comprising a normally inoperative electric discharge device, an output circuit for said discharge device, a resistor and capacitor in said circuit,

means for charging said capacitor through the resistor, means for inductively coupling a sound reproducing device to said output circuit, means for rendering said discharge device operative for discharging said capacitor therethrough, and

' means providing a low impedance path for surges around said resistor to produce pulses across the sound reproducing device when said capacitor is recharging.

3. A pulse circuit of the characterdescribed comprising a normally inoperative gas electric discharge'device, an output circuit for said electric discharge device including a capacitor for discharging through the discharge device when I it is operative, a source of charging current for the capacitor, and a resistor for coupling said source to the capacitor, means for rendering said discharge device operative, and an inductance in the output circuit of said discharge device for lowering the anode potential of said discharge device to cutoff after it is rendered conductive, a sound reproducing device coupled to the output circuit and responsive to surges therein for providing audible indication of the operation of the circuit.

4. A pulse circuit of the character described comprising a normally inoperative gas electric discharge device, an output circuit therefor including a source of electrical potential, a capacitor, and a resistor for feeding a charge from said source to said capacitor, means for coupling a sound reproducing device in said output circuit, means for rendering the discharge device operative for discharging the capacitance therethrough, an inductance interposed in said output circuit between said discharge device and said capacitor for lowering the potential across the discharge device below cutoff during the operation thereof, and means providing a low impedance surge path about said resistor for actuating the sound reproducing device in response to the operation of said discharge device.

5. A pulse circuit of the character described comprising a gas electric discharge device having a control electrode, an

source of electrical potential for feeding the capacitor, a sound reproducing device coupled to the output circuit, means for applying a potential to the control electrode for causing said discharge device to periodically conduct, and a condenser shunted across said resistor for providing a low impedance path to surges whereby said sound. reproducing device is actuated in response to th operation of said discharge device. j

6, A pulse circuit of the character described.

comprising a gas electric discharge device having a control electrode, an output circuit including a resistor and capacitor, a sourceof electrical potential for periodically charging said capacitor through the resistor, a sound reproducing device,

coupled to the output circuit, means for impressing a potential on said electrode for periodically firing said discharge device to discharge said capacitor and actuate the sound reproducing device, and inductive means interposed in the output circuit for carrying the potential across the discharge device below the quenching point during the operation of the discharge device.

'7. A pulse circuit of the character described comprising a gas electric discharge device having a control electrode, an output circuit includinga resistor and a capacitor, a source of electrical. potential for supplying a charge to the capacitor through said resistor, a sound reproducing de-- vice coupled to the output circuit, means for im-- pressing a potential on the control grid of said discharge device for rendering it periodically operative, and means providing a low impedancepath for surges about said resistor when said.

potential for supplying charge to said capacitor 7 through the resistor, a sound reproducing device inductively coupled to the output circuit for reproducing surges therein, means for impressing a potential on said electrode to periodically render said discharge device operative, an inductance interposed in said output circuit adjacent the discharge device for lowering the potential thereacross to the quenching point during its operation, and means providing a low impedance surge path across the resistor for accentuating the response of the sound reproducing device.

9. A pulse circuit of the character described comprising a gas electric discharge device having a control electrode, an output circuit including a capacitor and a resistor, a sound reproducing device coupled to said output circuit, a storage capacitor of greater capacity than said first capacitor for feeding a charge to said first capacitor through said resistor and the coupling of said sound reproducing device, a source of electrical potential for supplying the capacitors, means for impressing a potential on said electrode to periodically render said discharge device operative for discharging said first named capacitor therethrough, an inductance in said output circuit for lowering the potential across the discharge device below the quenching potential during its operation, means providing a low impedance surge path about the resistor for accentuating the. actuation of said sound reoutput circuitincluding resistor and a capacitor fed therethrough, a

producing: device; iria. response. to; the operation; of they electricz dischargeidevice, and. means lfcr measuring: the; current from H said source tomliecapacitorsras thesresultzof the; operation of the; electric discharge device.

1a. A; pulse circuit; of. the: character. described comprising a gasaelectric discharge device having a control. electrode,van output. circuit; including a capacitor and a resistorza storage. capacitor of t'enti-alfor supplying thev storage capacitor, means; for; applying a pctential fto said: electrode, for

periodically: firing the electric discharge; device, toxdischarge said: first capacitors theretnrough;

and-means; providing :a-low impedance. surge pathacross the resistorv for accentuating the response: A

of the sound reproducing device.

CHARLES R. MARSH;

REEEB/ENQES mm The following references are. of recordeinthe.

file of this patent:

UNII Q IATES EATEN IS.

umbe ame te.

2,1 742 La Pie re;

.9 65,7 3 Kalb et al Dec, 25,1944} 2362mm ic be OTHER REFERENCES Publication on page 157, ExperimentalE leco cs y Muller. Ger an androg ;.pub i h 19.42, Prentice ,Hall.

Publicationfl pa s 887 9,, Elec r cs Indus: tries, S pt; 19f ,Ra li0a9.t i y Meter, en.

Nuclear. Resear h! 

